This week, in middle-of-nowhere Utah, a NASA contractor tested the rocket booster that will get future astronauts to deep space. I went.

That's what astronaut Stanley Love told me on Monday, a day before the test of a rocket booster that will propel the space shuttle's successor into the void. An executive at Orbital ATK, the company that built the booster, also told me that if I wore loose pants, they would wave in the wind from the blast. I wasn't sure whether to believe them or to consider their statements the inadvertent propaganda of the excited.

Not that I wasn't excited for Tuesday's test. I was. I grew up watching shuttle launches from my backyard in Central Florida, about an hour from Kennedy Space Center, but I hadn't ever been this close to explosive rocketry. The test, in which Orbital ATK would fire the booster for two minutes, until its propellant ran out, would occur just over a mile away from the viewing area.

In the future, two boosters exactly like this one will provide around 80 percent of the lift that NASA's Space Launch System rocket—and the Orion habitat that will soon(ish) be packed with humans and astronaut ice cream—from the ground. For every second of their mayfly-short life, the boosters will eat through 5.5 tons of propellant. Once spent, they will dive from the main rocket's sides back down to Earth. The rocket itself will continue to fire, carrying future astronauts to deep-space destinations.

For this test, though, the booster was battened down to the ground, held horizontal so that it fired into a hillside and stopped from doing the one thing it wants to do: move.

*

The next morning at 5:00 AM, Highway 83—a two-laner running to and from Promontory, Utah—was already busy. Locals were already setting up umbrellas and Coleman grills on the side of the road, making breakfast and waiting for the 8:05 AM skyfire.

There's not a whole lot to see on 83 besides desolate desert mountains and patches of salt. It's beautiful in the way of Mars. But then a sign of life rises from the sagebrush: Rocket site, it says. It's the only hint that you'll soon come upon a giant aerospace complex, plopped on a hillside.

"You want to make rocket motors in the middle of nowhere where you don't disturb anyone," Kent Rominger, a former astronaut and current vice president of strategy and business development at Orbital ATK, explained in a briefing.

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A few miles after the sign, a "rocket garden" of old space-tubes does appear, as do the neutrally colored buildings where engineers make new versions of such things. Some buildings' sides have building-sized American flags painted on them; one has a roof-high radiation symbol.

Inside this architecture, engineers construct the SLS boosters and concoct the propellant, which begins as a Play-Doh-like pseudoliquid and hardens into the consistency of a (highly flammable) pencil eraser.

I sat in a viewing area at Orbital ATK's complex as the Sun rose, its rays growing hotter and hotter as we waited for the booster test through an hour-long delay resulting from a computer glitch. In those extra 60 minutes, I began to feel the anxious kind of excitement a person endures in line for a new roller coaster. What does it feel like to have your fillings rattled? What does it mean to witness the destruction of 1.5 million pounds of propellant? Were my jeans loose enough to wave in the wind?

Engineers fixed the computer, and the countdown resumed. And when the red numbers approached single digits, a voice from the sky (okay, from speakers) boomed over the crowd, a gathering of NASA and Orbital ATK employees who had worked on the booster, aerospace officials of all sorts, and current and former astronauts.

For Love, this was a particularly powerful moment. Someday, he very well could ride on the Space Launch System and feel this booster not from a mile away but from just below his body.

I put my camera down and just watched. It was raw power, refined.

Everyone, wearing complementary Orbital ATK ballcaps to block the Sun, stared at the hillside where the booster was bolted. At T-minus three seconds, two seconds, one, it was inert, plain, looking from a distance like a segment of some oil pipeline.

But just after the clock reached zero, a cone of fire shot from the booster, turning it into something else. A monster? A god? Definitely something alive. The cone grew, then stabilized, keeping its shape as new fire flowed out, like a river. But a silent river.

The sound did not reach the viewing site for a few seconds. But as a cloud of smoke began to rise, the sound—pressure waves, remember—pounded over us, its volume amped up because the booster was firing against a hillside, which pushed more pressure waves back at us. Love's words, and the executive's assertion, whispered creepily in my head. Rattle your fillings, ruffle your trousers.

I had time to think of all this because the river of fire just kept flowing. Which was strange. Because it is an explosion, albeit a controlled one, you expect it to boom and then stop like a bomb, like every other explosion you have seen. I put my camera down and just watched. It was raw power, refined.

*

Someday, two of those raw, refined boosters will fire not into a bunch of desert dirt but into a launchpad, propelling humans into space. The US government hasn't been able to launch its own astronauts into space since 2011, when the shuttle program ended. But the SLS will change that, and send them farther than ever before.

These boosters use shuttle components, although Orbital ATK reengineered a lot of their innards and added another segment to give them more thrust. The company that is now part of Orbital ATK (but was once just ATK and, before that, Morton-Thiokol and, originally, simply Thiokol) also made the shuttle's boosters. That, and the specifics of the June 28 test, bring back a tragic memory for the company.

On January 28, 1986, the temperature at Kennedy Space Center was around 28° F, colder than any previous launch. Officials decided to launch the Space Shuttle Challenger anyway. Seventy-three seconds after liftoff, the craft broke apart, killing all astronauts aboard.

An investigation called the Rogers Commission revealed administrative, cultural, and interpersonal problems that contributed to the disastrous decision. But from a technical standpoint, the cold had crippled the rubber O-rings that held the boosters' segments together, and the failed O-rings had caused the failure of the shuttle.

I thought of these O-rings during the test in Promontory, while the booster continued pouring fire into the landscape. Because while it was quite hot outside, the event was actually a "cold test," meant to see how the booster will behave at around 40° F, the lowest temperature it can be conditioned, which is 12° F warmer than its launch temperature. (After being fired, the booster cranks up to around 6,000° F—hot enough to boil steel.) Engineers had housed it in a hyper-air-conditioned building since April, chilling it to the core to get it down to the low end of its temperature range and see if it would hold up.

No one, in my two days on site, mentioned this connection to the past, and I didn't ask. Even if it probably would have been the responsible journalistic thing to do, I didn't want to inquire about their worst day on these so-far happy ones. It's a painful part of history—the company's, NASA's, spaceflight's, lots of individual human beings'—and one that could have been avoided. Still, I could not have been the only one thinking of Challenger.

"You're never going to get all the unknowns out of it."

Safety and chopping down risk are always on NASA's and Orbital ATK's front burners. Signs everywhere at the Promontory site say so. Even the free hats they gave us say, "Test before flight."

Love wants to fly, and he knows that to fly means to accept risk. "You're never going to get all the unknowns out of it," he says. "NASA promised to make [SLS] 10 times safer than the shuttle, but that's not possible with the technology."

If he gets the chance, he'll go. And with SLS, he and astronauts present and future will have more destination options.

*

The SLS will be the most powerful rocket ever, capable of carrying meatbags to lunar orbits, asteroids, and Mars. The Orion capsule, which will sit tiny atop the rocket like the finial on a flagpole, is the place the space-faring humans will live, work, play, and probably also cry and fight.

NASA has planned SLS's first mission for late 2018. Crewless, the system will go around the Moon and then come back home. Four years later, NASA plans to use SLS to launch a probe to Jupiter's moon Europa, to learn about its crusty ice sheet, the ocean that lies beneath it, and where best to land a future life-seeking rover.

And then, later in the 2020s, SLS will get its first passengers—a four-person crew, shot around the Moon. A few years later, another crew may explore an asteroid previously tugged into lunar orbit, as part of the Asteroid Redirect Mission. NASA bills these activities as preparation for SLS's eventual trips to Mars—they are testing their system and their humans in harsh environments far from Earth. It is all part of the#journeytoMars.

The missions' utility and momentum vectors have still drawn criticism, as has the lack of more missions and the design and contracting of SLS. The Verge called it "the rocket without a plan," while NASA Space Flight noted two years ago that the agency is "searching for missions to solve flight-rate dilemma." Twitter complains that NASA is on a #journeytonowhere. NASA's former deputy administrator Lori Garver said in 2014 that NASA should cancel SLS.

But Bill Hill, deputy associate administrator for exploration systems at NASA's headquarters in Washington, DC, considers the SLS's current design to be the best, and most cost-effective, of the options they investigated. He admits an existential threat to SLS is possible, especially because of the upcoming presidential change. The president provides Congress with a budget request, and Congress has to amend (or not) and then pass that federal budget. Projects and programs can technically get cut any time. The Obama administration, for example, killed the future-human-spaceflight program that preceded SLS, called Constellation, in fiscal year 2011, after four years of development.

Hill feels good about the administration transition, however. He believes that SLS is demonstrating and delivering on its promises, and says that the team has good, concrete stuff to show for themselves. "We've got a lot more there," he says.

This test, this booster and its futile flaring, are part of that there.

*

After two minutes of rocketfire, the cloud of smoke had grown apocalyptic, but the flames started to subside. The roar quieted. The fillings stopped rattling. People put down their cameras and looked at each other, then back out at the rising grey residue of space success.

Even if you were skeptical of NASA's plan and some of its ways of working, and even if you didn't much like to have moments of high emotion in public, it would be impossible to feel stoic about such a show of power—and here I guess I am talking about myself. The booster may have remained unmoved, but I didn't.

We did that, I thought. We're going places.

And the people around me had actually done that. Some of them might actually be going to those places.

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The viewing area cleared out fast, people going back to their lives, or home to relax, or out to celebrate. Although they might slack for a day or two, that won't last long. "Next week, we're all going to still keep working," Bruce Tiller of NASA's Marshall Space Flight Center in Huntsville, Alabama, told reporters.

But Mike Fuller of Orbital ATK did say of the test, pardoning his own pun, "It reignites the enthusiasm." The day-to-day of any job can wear on a person. But knowing your job results in Tuesdays like this one, which result in human space exploration, it reminds you, he said, "Oh, that's why I'm working here."

The smoke continued to drift and dissipate, some heading in the direction of the Great Salt Lake, not many miles but a long drive down a washboard gravel road. If you travel along that road, you'll hit the Golden Spike monument before you hit the lake.

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In May of 1869, right here in Promontory, the railroad system became transcontinental. A train and its track from the eastern side of the country faced off with a matching set from the western side. The two were separated by ground the length of just one missing railroad tie. The Reverend John Todd literally married the two tracks, joining them with some nice words and a spike of gold.

Wedding the lines was a small, ceremonial step. But having them be wedded was a giant leap not just in human travel, but also for our conception of what distances are insurmountable. A human could cross the continent in a reasonable amount of time. That human could also go home again.

If you keep driving, you'll go past ranches and ranches until you hit the shore, which is an otherworldly bed of salt that extends a couple hundred yards toward the water. And if you trek out to that water, you'll see how halophilic microbes have turned the liquid pink. Watermelon waves wash over bulbous, fractal salt structures. Small cliffs of crystal crumble into the tinted water when you step on them.